This research program is concerned with several fundamental aspects of the interrelationships between photopigments, neural organization, and visual behavior. One approach to analyzing these relationships is to utilize selected animal models that offer unique advantages that are often difficult to achieve in direct studies of human vision. The most prominent of these models is the New World monkey Saimiri sciureus (the squirrel monkey). This genus has a striking color vision polymorphism; the variant forms of this polymorphism have been much studied and they provide useful models for several aspects of human color vision. Research to be conducted falls into two major areas: (1) Development of the mechanisms underlying color vision. This research will seek to answer questions of how the neural connections necessary for color vision develop. To accomplish this a series of behavioral evaluations of simple and complex aspects of color vision will be conducted in squirrel monkeys, a species in which the relationship between X-chromosome gene action and photopigment specification allows the possibility of separating genetic and environmental influences in the development of short wavelength cone signals. In humans and other mammals the short-wavelength cone mechanism is relatively ineffective during the early development of color vision. This research will involve studies of the dichromatic ground squirrel to determine whether the source of that ineffectiveness is receptoral or a postreceptoral. (2) Investigations will be made of three fundamental aspects of the spectral properties of mammalian cone pigments. One investigation will collect and then examine spectra measured electrophysiologically from a large number of mammalian cone pigment types to determine if there are restrictions on the spectral positioning of mammalian cone pigments and, if so, what these restrictions are. A second investigation will seek to determine how much of the well-documented variations in cone- pigment based behavior, for example in human color matching, can be attributed to individual variations in cone pigment spectra. To accomplish this, electrophysiological measurements of cone spectra will be made in human protanopes. The experiment will be so designed that individual variations in cone spectra will be distinguishable from other sources of variation. A third investigation will seek to establish whether one form of human color vision defect, protanopia, can arise from more than one middle wavelength sensitive pigment. Preliminary results suggest that there may be polymorphic variants leading to protanopia.